Interior - Photometric & Sunlight Radiosity

[Eric]

I've been looking around on the net for tutorials that help to crack the code to radiosity in Viz4. With no luck. At least, no useful luck.

 

I'm trying to setup an interior scene with photometric lights and a sunlight system coming in through the windows. I'm having trouble balancing the intensity of the interior lights and the sunlight.

 

For example, if the sunlight is set to 90,000, and my interior lights are at 1,500, and I set my radiosity Physical Scale to 90,000, and when I render the scene it's totally over-lit, so I drop the intensity down to 45,000 (or cut the multiplier in half), do I have to change the Physical Scale to 45,000?

 

Are there tutorials or books out yet that go into depth about Radiosity in Viz4 yet?

[ZepSOFD]

Eric,

 

Physical Scale controls several things the three top items are:

 

Non-Physical based Lights (basically non-photometric lights there maybe more, but I'm not trying to cover everthing) - gives them a value roughly in candelas, that the radiosity engine can understand.

 

Reflection Intensity - if the PS is to low the reflection will appear dim.

 

Self-Illumination - if the PS is to low the Self-Ill. will appear dim or muddy.

 

These are some of the simple things that the Physical Scale will control.

 

If you are trying to light the scene with a combination of Standard and IES lights, than the Phy.Sca. value will be critical. If you are using IES Daylight and IES lights in the interior your exposure control will most likely save your bacon. But remember if your exterior is at 90k and you total interior per room with a small window is only 5 or 10k the rad. engine will produce an overbright exterior to a dark interior, not until those values come closer to equal will the camera exposure register a nice change in lighting levels between the int. and ext. of your image.

 

I hope that this wasn't to far of course from your post.

 

If anyone can add/correct I would appreciate it.

 

tom

[Eric]

Okay, so if my daylight system comes in with a scale of 90k, and my photometric lightbulb powering the lamp sitting on my end-table has a default scale of 1500, I need to crank the lamp bulb up to like 50k so the two are able to better illuminate the interior scene?

 

Is this basically to say there is no scientific hard and fast way of figuring out the numerical values of each photometric light's scale in relation to each other when using exterior/interior lights?

[abicalho]

Eric,

 

Physical Scale will do nothing to your lights. All it does is affect Raytrace and Self-Illumination.

 

Your problem is that you are expecting to see a "nice" rendered image, but if you look around when there's Daylight coming through a window at full power, the internal lights make no difference because the daylight is a lot more powerful.

 

Take a look at other posts in the forum related to Daylight, or on the 3dsmax forum.

 

Alexander

 

[ November 06, 2002, 09:02 PM: Message edited by: abicalho ]

[ZepSOFD]

A.B.,

 

This is directly out of the help file, is this not true when using standard lights with radiosity?

 

"Each standard light's Multiplier is multiplied by the Physical Scale value to give a light intensity value in candelas. For example, with the default Physical Scale of 1500, a standard omni light is treated by the renderer and radiosity as a photometric isotropic light of 1500 candelas."

 

Eric,

 

"Okay, so if my daylight system comes in with a scale of 90k, and my photometric lightbulb powering the lamp sitting on my end-table has a default scale of 1500, I need to crank the lamp bulb up to like 50k so the two are able to better illuminate the interior scene?"

 

In theory yes but in reality it really depends on what you want your final output to look like. If you want a nice lighting level for your interior and you want everything viewable thru a window to be blown out you need to have a light with a high value outside and a light with a low value inside and adjust your exposure control for the inside. If you want a nice level for your interior and a level that makes your exterior viewable you need to some how equalize the two values. Most likely you will not increase the interior value, you will decrease the exterior value closer to the interior value and adjust the exposure control for the interior again. This is because you are working with a Single Camera Exposure Control, this is not your eyeball which can take the two intesity levels and adjust them in less than a blink of an eye to a seemingly equal level that your brain will accept as correct.

 

I place my daylight system set the time, date, location then switch to manual and adjust the sun light intensity to suit. I have also read of people rendering twice one for interiors and one for exteriors and compositing them together. I'm sure if you seach around you will find other methods that work for you.

 

tom

[abicalho]

Answering your question:

 

This is directly out of the help file, is this not true when using standard lights with radiosity?

 

"Each standard light's Multiplier is multiplied by the Physical Scale value to give a light intensity value in candelas. For example, with the default Physical Scale of 1500, a standard omni light is treated by the renderer and radiosity as a photometric isotropic light of 1500 candelas."

 

The Daylight system does NOT use Standard Lights, so this does not apply.

 

Alexander

[Pierre-Felix Breton]

The daylight object can use IES sin/sky or Standard lights. Depending on which one is selected, the physical scale will apply with radiosity and exposure control.

 

As for the "exterior too bright with interior lights", make sure you use the daylight in Manual mode. You will be able to "dim" the Sun and Sky to get the results you want.

 

This is cheating on the "physically based" calculation but it should work for you.

 

Regards,

[Eric]

Thank everyone for all your input. One of the things I've noticed is that I need to light the interiors with a default material applied, and no daylight system, until I tweak the interior lights. Then, once the brightness level is achieved, I can then start applying materials in groups of 2 or 3, processing the radiosity quickly and testing the rendering for excessive color bleeding. I've noticed floors are really bad about bleeding once the sunlight hits them, so even more adjustments to mats will be necessary when the daylight is placed and active.

 

I agree with one of the other posts I've seen on this site, that VIZ needs to incorporate presets for different types of mats for the reflectivity, as was in Lightscape. Is it possible for someone to create a script of something like this that will generate a material with the proper settings?

[ZepSOFD]

A.B.,

 

I concur that the PS does not effect the daylight system(well technically it does because if you use a standard light in the daylight system the multiplier of the standard light is linked to the PS and will change so it can maintain a preset light value for the daylight system). But for non-p based lights (with the exclusion of the daylight system) the PS is multiplied by the standard light mulitplier as the manual says.

 

P-F. B.,

 

"This is cheating on the "physically based" calculation"

 

When using the IES Sun set to manual why is this cheating?. The sun has a range from the highest high to the lowest low based on your current location, date, time, and atmospheric conditions. With atmospheric conditions leading the way in controlling the majority of light that reaches the earth. Since VIZ only allows three preset atmospheric conditions per T,D,L, why not set the light to manual to cover any other conditions, if it will help the overall image quality, but then again how would changing the sun intesity manually be any different than using the three existing presets.

 

Eric,

 

Using default materials to tweak your lighting is almost a waste of time and should be basically used to check things like model deficiencies (light/shadow leaks, backfaces) and/or material placeholders until preliminary material selections are made. If possible build your materials first and apply, it will save you time down the line when light tweaking w/radiosity because the rad. sol. is totally effected by the values assigned to the materials.

 

tom

 

[ November 08, 2002, 02:36 PM: Message edited by: ZepSOFD ]